Field of the Invention
The invention relates to a burner with an axis and a configuration being rotationally symmetrical relative to the latter and including an outer casing and an inner casing coaxial thereto, the configuration defining an annular gap extending from an inlet to an outlet for guiding a stream of oxygen-containing gas, a multiplicity of nozzles disposed in the annular gap for supplying a fuel and a swirl lattice disposed in the annular gap.
The invention relates, in particular, to such a burner for use in a gas turbine.
A burner of that type is disclosed in European Patent 0 193 838 B1, corresponding to U.S. Pat. Nos. 4,701,124 and RE33896 and in an article entitled "Eine wirtschaftliche Losung des NO.sub.x --Problems bei Gasturbinen" [An Economical Solution to the NO.sub.x Problem in Gas Turbines] by H. Maghon, VGB Kraftwerkstechnik [VGB Power Station Technology] 68 (1988), 799. A development of that burner emerges from International Publication WO 92/19913 A1, corresponding to U.S. Pat. No. 5,451,160.
European Pat. Application 0 589 520 A1, corresponding to U.S. Pat. No. 5,381,652, as well as U.S. Pat. Nos. 5,165,241; 5,251,447; 5,323,604; and 5,351,477 are also of interest in that connection. Reference is also to be made to an article entitled "Dry Low NO.sub.x -Combustion Systems for GE Heavy-Duty Gas Turbines" by L. H. Davis, Prospectus GER-3568c of GE Industrial and Power Systems, Schenectady, N.Y. Burners or combustion parts with burners for use in gas turbines emerge from all of those documents.
In the case of the relevant teachings of fluid mechanics which are important in the present connection, attention is drawn to a book entitled "Ventilatoren" [Fans] by B. Eck, 5th edition, Springer-Verlag Berlin, Heidelberg and New York 1972, Chapter C, pages 283 to 285, and a book entitled "Axialkompressoren" [Axial compressors] by J. H. Horlock, Verlag G. Braun, Karlsruhe, Germany, 1967, Supplement 4.
Both books relate to fans, particularly fans of the axial type, which are distinguished by a rotating swirl lattice which sucks in a stream of gas in the form of a swirl-free stream along an axis and discharges it in the form of a swirling accelerated stream along the axis. In a burner of the type described, there is a stationary swirl lattice, against which a swirl-free stream that is accelerated in another way flows and from which the stream is discharged with a swirl and with some pressure loss. The configuration of the burner is therefore similar in many respects to the configuration of a fan, and essential theoretical principles of a fan are directly applicable. An effect which occurs on any stream of gas advancing with a swirl along an axis, irrespective of the way in which that stream has been produced, is particularly important in the present case. That effect is the formation of a vortex core within the stream, that is to say a stream advancing with a swirl is inclined to assume the form of an annulus, so that in a central region of a cylindrical tube in which the stream is guided, the central region surrounding the axis, there is no longer any flow in the direction of the stream.
The stream of a gas through a largely randomly selectable configuration of limitations, in particular through a burner, can be calculated through the use of numerical mathematics, for which purpose appropriate computer programs have in the meantime been offered on a commercial scale. Such computer programs are known to persons who are experienced and active in the relative field by the names TASCFLOW and FLUENT.
A burner of the type mentioned in the introduction in general serves the purpose of burning a fuel reliably and with low pollutant emission in a stream of oxygen-containing gas, in particular in compressed air. Premixing combustion has proved to be beneficial to avoid the formation of pollutants, such as nitric oxides and carbon monoxide. For that purpose, initially as homogeneous a mixture of fuel and oxygen-containing gas as possible is formed, and only that mixture is burnt. For such a mixture, there is in general the possibility of premature ignition, in particular under the conditions which are to be expected in a gas turbine and especially when a relatively easily combustible fuel or one with high flame velocity is to be used. Fuels of that type are, for example, gases which contain elementary hydrogen, for instance gases which are obtained by coal gasification, and natural gases that have high proportions of longer-chain hydrocarbons, wherein the ignition temperatures thereof are clearly lower than the ignition temperature of methane.
In a burner in which such premixing combustion is carried out, as is described in some of the documents mentioned above, in particular in European Pat. 0 193 838 B1, corresponding to U.S. Pat. Nos. 4,701,124 and RE33896, and International Publication WO 92/19913 A1, corresponding to U.S. Pat. No. 5,451,160, further problems may arise if the flow to the burner is not ideal and the mixing of the oxygen-containing gas with the fuel is thereby impaired. In such a case, an inhomogeneous temperature distribution and, correspondingly, an increased production of nitric oxides result during the combustion of the mixture. Furthermore, an inhomogeneous mixture is conducive to premature ignition. Those considerations plainly stand in the way of implementing premixing combustion in a gas turbine, in which an easily combustible fuel is to be burnt. They also show that premixing combustion, such as it has been possible to carry out heretofore, has not been free of problems, particularly because premature ignition of a mixture of fuel and oxygen-containing gas can relatively easily cause serious damage to an affected burner.